In the manufacture of soft tissues, such as facial and bath tissues, the industry has continually improved the tactile characteristics of the products to meet the needs and desires of consumers. One means for improving the feel of tissues is to incorporate an additive into the tissue, including a silicone such as a polysiloxane. The term "silicone" includes a wide range of products having chains of silicon atoms as their core structure. Different properties are achieved by the attachment of selected chemical functional groups to the silicone backbone. The resulting structures are commonly referred to as polysiloxane, polydimethylsiloxane, or polydiorganosiloxanes. Silicones are usually hydrophobic and can be obtained as neat fluids, organic solvent solutions, or as water emulsions. These emulsions can have a positive, neutral, or negative charge. The size of the emulsion particle can also be adjusted from about 50 nanometers (micro-emulsions) to about 1 micron. Silicones can be supplied as a fluid, but these usually have low solubility in water unless an additional functional group is used to add hydrophilic character.
Silicones are known to provide a desireable smooth or silky feeling to the surface of the tissue and thereby improve perceived softness. Typically silicones are applied to the tissue web at some point after it is formed, either before or after drying, by spraying or printing the silicone onto the surface of the tissue. While such methods are effective, they require a capital investment in spraying or printing equipment to apply the silicone. Also, the silicones themselves are expensive and a significant amount of silicone is generally required to impart the desired properties to the tissue. Add-on amounts typically range from about 1-2 dry weight percent based on the weight of the fibers.
The concept of adding silicones to the wet end of the tissue making process has been previously considered because of its simplicity and attendant avoidance of capital equipment. But when used in significant amounts as are ordinarily required by spraying or printing, the silicone wreaks havoc with the downstream creping operation by preventing adequate adhesion of the sheet to the dryer surface and thereby causing the sheet to flare off of the dryer. In addition, the silicone rapidly builds up in the wet end water system, which must be disposed, resulting in the loss of the expensive silicone.
Hence there is a need for a means of incorporating silicone materials into tissues which improves the tactile properties of the tissue and which is simple and relatively inexpensive in terms of capital and materials costs.